This project will identify basic mechanisms underlying age-related changes in languages - and sequencing in behavior. The experiments test two general accounts of cognitive aging, Transmission Deficit hypothesis and the Inhibitory Deficit hypothesis, and promise to fill in our knowledge regarding relations between aging and comprehension, conceptual error detection, word retrieval, speech errors, and other aspects of language production. The main long-term goal is to help develop well specified theories of aging that apply to a broad spectrum of cognitive performance, and address applied issues related to why older adults commonly experience difficulty in retrieving information, producing speech, and encoding new information in everyday life. Unlike previous approaches focusing primarily on cognitive declines, this project also examines cases where older adults: are predicted to exhibit superior performance to young adults. Five sets of experiments are proposed. Experiments 1-5 investigate effects of aging on the on- line perception of phonology. Experiments 6-8 examine age-linked changes in the ability to encode words and sentences under time pressure. Experiments 7-14 compare effects of aging for participants carrying out directly comparable perception versus production tasks in order to understand age-linked asymmetries between language production and perception, e.g., age-linked declines in word retrieval versus robust comprehension of the same words. Experiments 15-17 are the first to explore effects of aging on the extremely general problem of serial order in the organization of behavior. Experiments 18-23 examine effects of aging on miscomprehensions and the ability to detect conceptual errors.